Small bone tapered compression screw

ABSTRACT

The present invention relates to a device and system for surgical fixation of small bones, small bone fragments, and osteotomies and more particularly to compression screw having an elongated and spiked tapered threaded leading portion which is joined to a section that is free from threads and a threaded trailing portion and more sharply tapered head which has threads that continue from the threads of the leading portion.

FIELD OF THE INVENTION

The present invention relates to a device and system for surgicalfixation of small bones, small bone fragments, and osteotomies and moreparticularly to compression screw having an elongated and slowly taperedthreaded leading portion which is joined to a section that is free fromthreads and a threaded trailing portion and more sharply tapered headwhich has threads that continue from the threads of the leading portion.

BACKGROUND OF THE INVENTION

Patients often suffer from late stage arthritis in phalangeal joints ofthe hands and feet, and this presents a variety of challenges forattending physicians. While current treatment protocols usually provideacceptable results, there is a likelihood of straight distalinterphalangeal joint fusion which provides for sub-optimal outcomes.Research has shown that when a patient's distal interphalangeal joint isfused in a functional position, finger dexterity and grip strengthimprove over that of a patient with a straight fusion. Physicians canachieve angled fusions by using k-wire fixation, however, thisimmobilization protocol can fail, and lead to several complications andvaried results. While the utilization of compression screws can providereliable, strong repairs, it does not offer the additional benefit offunction flexion which is provide by a properly angled and orientedimplant fixation device, especially one, which provides the addedbenefit of compression across the joint during fusion.

Advantageous locations the use of the present invention is in thephalanges of the hand or foot. In each finger, there are three phalangesthat are separated by two joints called the interphalangeal joints (IPjoints). The proximal IP joint (PIP joint) is the one closest to the MCPjoint. The other joint closest to the end of the finger is the distal IPjoint (DIP joint). The thumb just has one IP joint. The joints arecovered on the ends with articular cartilage. The foot has an analogousstructure substituting the large toe for the thumb. It should beunderstood that there may be additional surgical techniques or locationsin the body where the device of the present invention may be suitablefor use.

SUMMARY OF THE INVENTION

The present invention solves the problems associated with performing afusion technique or an osteotomy, in particular in the interphalangealjoints. The device of the invention is a compression screw having ashaft with a longitudinal axis along which there is a leading portionincluding a sharp spiked threaded tip, and an intermediate unthreadedportion, and a trailing threaded portion which joins the intermediateportion and the more sharply expanding or tapered head portion, whichmay include the same thread pitch, size and shape of the trailing shaftportion having a constant inner diameter and outer diameter.Alternatively, the trailing portion may have a lesser thread pitchcompared to the tapered tip. It should be noted while that the trailingportion may be considered to be proximal to the leading portion relativeto the screw itself, in use, the leading portion is intended to beimplanted more proximally relative to the joint than the trailingportion. Moreover, the head portion is configured to provide forcompression across the fusion joint, and to inhibit rotation of thecompression device in the interphalangeal position as the leadingportion is embedded into the intermediate phalange which is positionedat an angle with respect to the distal phalange. In addition, thepresent invention by provides for a percutaneous insertion in a surgicaltechnique with an intramedullary implant designed to minimize softtissue, cartilage and vascular damage upon insertion; and to facilitateearly, active mobilization post-operative protocols for acceleratedhealing and earlier return to work.

The head at the trailing end includes a driving recess, such as ahexalobe, capable of being driven by a suitable driver into the opening.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a device in accordance with theinvention;

FIG. 2 is a side cross-sectional view of the device of FIG. 1 takenalong the longitudinal central axis;

FIG. 3 is an end view of the head of the device from the trailing end;

FIG. 4 is an end view of the device from the leading end;

FIG. 5 is a detail of FIG. 2 showing the threads and the head;

FIG. 6 is a detail of FIG. 2 showing the top of the threaded leadingsection;

FIG. 7 is a detail of FIG. 2 showing the steeply tapered spike end ofthe screw of FIG. 2;

FIG. 8 is a dorsal view of a skeleton of a hand showing the implant ofthe invention in place in a PIP fusion;

FIG. 9 is an illustration of the step of inserting a guide wire in aretrograde fashion through the distal phalange in accordance with thetechnique of the invention;

FIG. 10 is an illustration of the step of inserting a guide wire in aretrograde fashion through the intermediate phalange in function flexionaccordance with the technique of the invention;

FIG. 11 is an illustration of the step of inserting and confirming theplacement of the implant across the fusion site in accordance with thesurgical technique of the invention;

FIG. 12 is an isometric view of a further embodiment of the device inaccordance with the invention;

FIG. 13 is a side cross-sectional view of the device of FIG. 12 takenalong the longitudinal central axis;

FIG. 14 is an end view of the head of the device of FIG. 12 from thetrailing end;

FIG. 15 is an end view of the device of FIG. 12 from the leading end;

FIG. 16 is a detail of FIG. 12 showing the threads and the head;

FIG. 17 is a detail of FIG. 12 showing the far end of the threadedleading section;

FIG. 18 is a detail of FIG. 12 showing the steeply tapered spike end ofthe screw of FIG. 12; and

FIG. 19 is a dorsal view of a skeleton of a hand showing the implant ofthe invention of FIG. 12 in place in a PIP fusion.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an exemplary embodiment 10 of the tapered compression screwof the present invention. The screw 10 may be formed of any suitablebiocompatible material, such as surgical grade stainless steel,titanium, alloys of nickel and chromium, nitinol, PEEK, hydroxyapatite,bio-glass or other bio compatible materials or combinations of thesematerials. The screw 10 has a first end, or trailing end (i.e. relativeto the screw, the proximal end), 12, a second end, or leading end (againrelative to the screw, the distal end), 14, a shaft 16 with an outersurface 17, and the shaft 16 including a slowly tapered spiked leadingportion (i.e. a long cone) 18 which includes a thread 19 and a terminalend 22. The leading portion 18 is joined to an intermediate portion ofthe shaft 20 which is free from threads and is joined to a trailingportion 24 of the shaft 16. The trailing portion 24 has threads 21 andjoins the leading portion 18 of the shaft to a compression head 30 whichalso includes threads 23 at the same pitch and shape as the threads 21of the trailing portion (although in a further embodiment, the threadpitch may be changed to achieve greater compression). The head 30 alsoforms a cone 33 that is threaded, and which joins the threadedcylindrical portion of the trailing section of the shaft 16. The head 30has a driving surface 32 in a drive recess 34 formed in the top of firstend 12.

The angle of the leading tapered area is from 4° to 12°, and preferably5-8° which is defined at the intersection of a line at the outer surfaceof the inner diameter of the leading area and the central axis and thecompression head has an angle which is similarly determined and is from5° to 16°, but preferably is 9-14°, and is at least 2° greater than thetaper of the leading end and extends for a distance longitudinally thatis 25% to 75% of the distance of the leading taper. Ideally, the leadingtaper extends for from 25% to 50% of the length of the screw, and theintermediate portion extends of 25% to 50% of the length and thetrailing portion of the shaft extends for 15% to 50% of the length ofthe screw and the head extends for 5% to 15% of the length of the screw,with the screw shaft nominally comprising ⅓ trailing portion, ⅓intermediate portion and ⅓ leading portion+/−5-10% for each portion.

The spiked end can be driven into the intermediate phalange at an angleto create the position of functional flexion. The aggressive taper onthe leading tip allows the screw to be used in facilitating angulationbetween two bone while still fitting into the bone, which the prior artscrews do not accommodate. The driving surface 32 of the head has ahexalobe drive configuration, although any suitable drivingconfiguration may be used. Other driving configurations that may be usedinclude slotted, Pozidriv, Robertson, tri-wing, Torq-Set, SpannerHead,Triple Square and hex head.

The leading and trailing portions of the device includes a thread whichis defined between the outer diameter and the inner diameter and cansuitably include a right handed single start thread with a pitch of from3-4, and preferably at 3+/−0.5 with a similar lead value. In the secondembodiment the tip pitch is from 0.9 to 1.0 mm and preferably0.95+/−0.02 mm, and the head pitch is from 0.70 to 0.85 mm, andpreferably 0.75 mm The trailing section and following profiles of thethreads together form an angle of 25° to 75° and preferably 30°+/−15°,and preferably +/−10°, and with a thread depth of 0.1 mm to 0.4mm+/−0.02 mm, and optionally a thrust profile or a traditional bonescrew buttress thread. There is a pitch differential between the threadsof the conical section of the head and the spiked taper of the leadingend of the screw, with the leading thread pitch being about 0.75 to1.25, but in any case, from 1.2 to 1.5 times the pitch of thecompression head, which is 0.5 to 1.0.

FIG. 8 illustrates a screw 10 in accordance with the present inventionin position across a first PIP joint to secure a fusion.

In FIG. 9, in a first step of a surgical technique in accordance withthe invention, the joint is scored for fusion and a guide wire 38 isinserted in the intramedullary cannel in retrograde until is abuts theinners cortical surface of the distal phalange,

In FIG. 10 the end of the finger is bent and the guide wire is insertedfurther into the phalanges to secure the distal phalange in a positionof functional flexion relative to the intermediate phalange. Acannulated drill can be used to drill a hole across the fusion site overthe guide wire.

In FIG. 11, the device 10 is driven into the opening in the phalanges bymeans of the drive recess. The outer diameter of the threads 28, isslightly larger than the inner diameter of the opening in the bone. Thisprovides bone material for threads 28 to thread into and provides atight fit for device 10.

FIG. 12-19 show a second embodiment 110 of the tapered compression screwof the present invention. This screw 110 has a first end, or trailingend (i.e. relative to the screw, the trailing end), 112, a second end,or leading end (again relative to the screw, the leading end), 114, ashaft 116 with an outer surface 117, and the shaft 116 including aslowly tapered spiked leading portion (i.e. a long cone) 118 whichincludes a thread 119 and a terminal end 122. The leading portion 118 isjoined to an intermediate portion of the shaft 120 which is free fromthreads and is joined to a trailing portion 124 of the shaft 116. Thetrailing portion 124 has threads 121 and joins the leading portion 118of the shaft to a compression head 130 which also includes threads 123at the same pitch and shape as the threads 121 of the trailing portion.The head 130 also forms a cone 133 that is threaded and which joins thethreaded cylindrical portion of the trailing section of the shaft 116.The head 130 has a driving surface 132 in a drive recess 134 formed inthe top of first end 112.

Having thus described some embodiments of the invention, othervariations and embodiments that do not depart from the spirit of theinvention will become apparent to those skilled in the art. The scope ofthe present invention is thus not limited to any particular embodiment,but is instead set forth in the appended claims and the legalequivalents thereof. Unless expressly stated in the written descriptionor claims, the steps of any method recited in the claims may beperformed in any order capable of yielding the desired result.

What is claimed is:
 1. A tapered compression screw for use in bonecomprising: a threaded tapered compression head having a torque drivingrecess, and a shaft having a threaded first portion joined to thecompression head and an unthreaded intermediate second portion and athreaded spiked third portion joined to the unthreaded intermediatesecond portion and forming a taper angle of from 3° to 15° along thecentral longitudinal axis of the shaft and being a length of from 25% to75% of the length of the shaft.
 2. The tapered compression screw as setforth in claim 1 wherein the thread of the first section and the secondsection is a buttress thread.
 3. The tapered compression screw of claim1 wherein the threaded tapered compression screw has a conical sectionand the threads define a compression head maximum major diameter, andthe threaded first portion has a thread that defines a first portionmajor diameter and compression head maximum major diameter is from 1.1to 1.5 times the value of the first portion major diameter.
 4. Thetapered compression screw of claim 1 wherein the threaded taperedcompression screw has a conical section head with an angle from 5° to12°.
 5. The tapered compression screw of claim 4 wherein the threadedtapered compression screw has a conical section head with an angle whichis 8°+/−2°.
 6. The tapered compression screw of claim 1 wherein thethreaded tapered compression screw has a conical section head with afirst length along the longitudinal axis of the screw and the spikedthird portion has a second length along the longitudinal axis of thescrew and the value of first length is 25% to 75% of the value of thesecond length.
 7. The tapered compression screw of claim 1 wherein thethreaded tapered compression screw has a third length which is anintermediate unthreaded portion along the longitudinal axis of the screwand the value of first length is 5% to 25% of the value of the thirdlength.
 8. The tapered compression screw of claim 1 wherein the threadedtapered compression screw has a third length which is an intermediateunthreaded portion along its longitudinal axis and the spiked thirdportion second length has a value of 50% to 100% of the value of thethird length.
 9. A tapered compression screw having along a longitudinalaxis, a threaded first portion which comprises a conical head and ashaft having a constant minor diameter, a unthreaded second portionwhich comprises a shaft having a constant minor diameter that is thesame as the minor diameter of the shaft of the first portion, and athreaded third portion which comprises a conical tip which has a sidewall at a smaller angle than the conical head.
 10. A tapered compressionscrew as set forth in claim 9 wherein the angle of the conical head isfrom 5° to 10°.
 11. A tapered compression screw as set forth in claim 9wherein the angle of the conical tip is from 10° to 15°.
 12. A taperedcompression screw as set forth in claim 9 wherein the first portioncomprises from 15% to 25% of the length of the screw.
 13. A taperedcompression screw as set forth in claim 9 wherein the second portioncomprises from 30% to 40% of the length of the screw.
 14. A taperedcompression screw as set forth in claim 9 wherein the third portioncomprises from 40% to 50% of the length of the screw.
 15. A surgicalmethod for facilitating fusion between an intermediate phalange and adistal phalange comprising the step of implanting a tapered compressionscrew having a spiked tip along the long axis of a distal phalange;placing the distal phalange at a selected angle relative to the longaxis of an intermediate phalange, and driving the spiked tip of thetapered compression screw into the intermediate phalange at the selectedangle.
 16. A surgical method as set forth in claim 15 wherein thetapered compression screw has along a longitudinal axis, a threadedfirst portion which comprises a conical head and a shaft having aconstant minor diameter, a unthreaded second portion which comprises ashaft having a constant minor diameter that is the same as the minordiameter of the shaft of the first portion, and a threaded third portioncomprising the spiked tip which comprises a conical tip which has a sidewall at a smaller angle than the conical head.
 17. A surgical method asset forth in claim 16 wherein the tapered compression screw includes anangle of the conical head from 5° to 10°.
 18. A surgical method as setforth in claim 16 wherein the tapered compression screw includes anangle of the conical tip from 10° to 15°.
 19. A surgical method as setforth in claim 16 wherein the first portion comprises from 15% to 25% ofthe length of the tapered compression screw.
 20. A surgical method asset forth in claim 16 wherein the second portion comprises from 30% to40% of the length of the tapered compression screw.
 21. A surgicalmethod as set forth in claim 16 wherein the third portion comprises from40% to 50% of the length of the tapered compression screw.